In a rectangular battery (hereinafter may be simply referred to as a “battery”), an electrode group and an electrolyte are accommodated in a battery case made of, e.g., metal. The electrode group is configured such that a positive electrode and a negative electrode are wounded or stacked with a separator being interposed between the positive and negative electrodes. The separator electrically insulates the positive and negative electrodes from each other, and holds the electrolyte. An opening is formed in the battery case, and is sealed by a sealing plate.
The sealing plate has the same polarity as that of the battery case. A through-hole is formed in a thickness direction of the sealing plate, and a terminal part having a polarity different from that of the battery case is inserted into the through-hole through a gasket. This electrically insulates the sealing plate and the terminal part from each other.
When great pressure which can deform the battery case is applied from an outside of the battery, the electrode group is deformed, and the separator is damaged. Thus, internal short-circuit occurs. When the internal short-circuit occurs, short-circuit current flows, and therefore Joule heat is generated. This results in heat generation of the battery, and, in some cases, results in overheating. In particular, a lithium ion secondary battery has a high energy density, prevention of overheating and improvement of safety have been required for the lithium ion secondary battery. In, e.g., Patent Documents 1-3, the following batteries have been proposed.
In the battery described in Patent Documents 1 and 2, a short-circuit unit is provided, which includes at least a first conductive unit which is formed of a conductor electrically connected to a positive electrode, a second conductive unit which is formed of a conductor electrically connected to a positive electrode, and an insulating holding unit configured to hold the first and second conductive units in a non-electric-contact state.
The battery described in Patent Document 3 has the structure in which, when mechanical pressure is applied toward an inside of the battery, a battery case and a current collector part (no active material is provided on the current collector part) positioned on the outermost of the electrode group come into contact with each other to generate electric short-circuit.